c_playground README & .gitignore update

Author: Nao-ris

.gitignore

@@ -1,2 +1,4 @@
 /target/
 Cargo.lock
+
+.vscode

c_playground/.gitignore

@@ -0,0 +1,6 @@
+CMakeCache.txt
+CMakeFiles
+Makefile
+cmake_install.cmake
+
+Main

c_playground/README.md

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+## Purpose of the c_playground
+
+Couchbase does not provide support for Rust bindings, so we cannot communicate code from this repo in support tickets.
+
+With the c_playground, you can code whatever you want in C with full access to the couchbase-lite-C API.
+
+## How to use it
+
+The code in main.c will be compiled.
+
+In the c_payground repository, you need to run the command once:
+
+```
+cmake CMakeLists.txt
+```
+
+You will then be able to compile the code anytime you want with the command:
+
+```
+make
+```
+
+The file Main is the executable, do not forget to set the execution right for yourself:
+
+```
+chmod u+x ./Main
+```
+
+Execute your code:
+
+```
+./Main
+```